Methods and apparatus for cyclic prefix reduction in MMwave mobile communication systems
To reduce the duration of a cyclic prefix used for a multiple input, multiple output (MIMO) communications channel, delay spread variations for different transmit/receive beam pair combination is estimated and used for fast beam switching and to support single user MIMO (SU-MIMO) even when the CP difference between two beams is large. Beam switching reference signals are employed to estimate delay spread exceeding current CP, and to support beam switching. CP covering sub-clusters within clusters for the MIMO channel are exploited to reduce the CP requirement and improve efficiency. Any one of a number of different CP durations may be selected for each different mobile station, using one of a finite set of subframe configurations for which the CP durations of different symbol locations within the subframe are predefined. Dynamically switching subframe configurations by the system accommodates high mobility.
1. A method, comprising:
inserting, by a transmitter, a beam switching reference signal in an Orthogonal Frequency Division Multiplexing (OFDM) signal for transmission to a mobile station in a Multiple Input, Multiple Output (MIMO) wireless communications system; and
estimating delay spread, of new beams, exceeding a current cyclic prefix of the OFDM signal using the beam switching reference signal,
wherein the beam switching reference signal comprises a plurality of different time domain Zadoff Chu (ZC) sequences each based on one of a plurality of different sequence roots, wherein the ZC sequences based on the different sequence roots are inserted between sets of contiguous resource blocks in time and frequency within the OFDM signal.
2. The method according to claim 1 , wherein the beam switching reference signal is a non-OFDM signal embedded into the OFDM signal.
3. The method according to claim 1 , wherein a beam width, a band width and a power of the beam switching reference signal are comparable to a Physical Downlink Shared CHannel (PDSCH) transmission.
4. The method according to claim 3 , wherein the beam width, band width and power of the beam switching reference signal are selected to allow estimation of a power delay profile (PDP) during data transmission.
5. The method according to claim 1 , wherein the beam switching reference signal has characteristics allowing synchronization in addition to delay spread estimation.
6. The method according to claim 1 , wherein the beam switching reference signal comprises cyclically shifted versions of a Zadoff Chu (ZC) sequence that are orthogonal to one another.
7. The method according to claim 6 , wherein the beam switching reference signal comprises a ZC sequence that is orthogonal to a ZC sequence within a beam switching reference signal used in an adjacent sector or an adjacent cell.
8. The method according to claim 1 , wherein the ZC sequences are interleaved over an entire band of the OFDM signal.
9. The method according to claim 8 , wherein guard tones or active interference cancellation (AIC) tones are inserted between the ZC sequences and OFDM tones formed by the sets of contiguous resource blocks.
10. The method of claim 1 , wherein estimating the delay spread of the new beams is performed by the mobile station, and
wherein the beam switching reference signal is configured to enable the mobile station to estimate, of the new beams, delay spread exceeding the current cyclic prefix of the OFDM signal.
11. A system, comprising:
a transmitter configured to:
transmit an Orthogonal Frequency Division Multiplexing (OFDM) signal to a mobile station in a Multiple Input, Multiple Output (MIMO) wireless communications system, the OFDM signal including a current cyclic prefix, and
insert a beam switching reference signal into the OFDM signal, wherein the beam switching reference signal is configured to enable the mobile station to estimate, of new beams, delay spread exceeding the current cyclic prefix of the OFDM signal,
wherein the beam switching reference signal comprises a plurality of different time domain Zadoff Chu (ZC) sequences each based on one of a plurality of different sequence roots, wherein the ZC sequences based on the different sequence roots are inserted between sets of contiguous resource blocks in time and frequency within the OFDM signal.
12. The system according to claim 11 , wherein the beam switching reference signal is a non-OFDM signal embedded into the OFDM signal.
13. The system according to claim 11 , wherein a beam width, a band width and a power of the beam switching reference signal are comparable to a Physical Downlink Shared CHannel (PDSCH) transmission.
14. The system according to claim 13 , wherein the beam width, band width and power of the beam switching reference signal are selected to allow estimation of a power delay profile (PDP) during data transmission.
15. The system according to claim 11 , wherein the beam switching reference signal has characteristics allowing synchronization in addition to delay spread estimation.
16. The system according to claim 11 , wherein the beam switching reference signal comprises cyclically shifted version of a Zadoff Chu (ZC) sequence that are orthogonal to one another.
17. The system according to claim 16 , wherein the beam switching reference signal comprises a ZC sequence that is orthogonal to a ZC sequence within a beam switching reference signal used in an adjacent sector or an adjacent cell.
18. The system according to claim 11 , wherein the ZC sequences are interleaved over an entire band of the OFDM signal.
19. The system according to claim 11 , wherein guard tones or active interference cancellation (AIC) tones are inserted between the ZC sequences and OFDM tones formed by the sets of contiguous resource blocks.
20. A system, comprising:
a transmitter configured to transmit an Orthogonal Frequency Division Multiplexing (OFDM) signal to a receiver in a Multiple Input, Multiple Output (MIMO) wireless communications system or the receiver is configured to receive the OFDM signal from the transmitter,
wherein the OFDM signal includes a beam switching reference signal inserted by the transmitter, the beam switching reference signal having at least one of:
a power corresponding to a single Physical Downlink Shared CHannel (PDSCH) symbol spread over a plurality of OFDM symbols, and
frequency domain signal characteristics enabling the receiver to estimate a power delay profile (PDP), and
wherein the beam switching reference signal is configured to enable the receiver to estimate, of new beams, delay spread exceeding a current cyclic prefix of the OFDM signal, and
wherein the beam switching reference signal comprises a plurality of different time domain Zadoff Chu (ZC) sequences each based on one of a plurality of different sequence roots, wherein the ZC sequences based on the different sequence roots are inserted between sets of contiguous resource blocks in time and frequency within the OFDM signal.
21. The system according to claim 20 , wherein a cyclic prefix for symbols within the OFDM signal covers a delay spread for all beams between the transmitter and the receiver.
22. A method, comprising:
transmitting data from a base station to a first mobile station in a Multiple Input, Multiple Output (MIMO) wireless communications system using a first beam pair, determining a delay spread for each of a plurality of different beams between the base station and the first mobile station using a beam switching reference signal inserted by the base station into an Orthogonal Frequency Division Multiplexing (OFDM) signal carrying the data; and
at least one of:
selecting a second beam pair of the plurality of beams on which subsequent frames of the data are transmitted from the base station to the first mobile station based on one or more determined delay spreads, and
setting a cyclic prefix to exceed each of the one or more determined delay spreads,
wherein the beam switching reference signal is configured to enable the first mobile station to estimate, of the second beam pair, delay spread exceeding a current cyclic prefix of the OFDM signal; and
wherein the beam switching reference signal comprises a plurality of different time domain Zadoff Chu (ZC) sequences each based on one of a plurality of different sequence roots, wherein the ZC sequences based on the different sequence roots are inserted between sets of contiguous resource blocks in time and frequency within the OFDM signal.
23. The method according to claim 22 , wherein the second beam pair has a delay spread greater than a delay spread of the first beam pair.
24. The method according to claim 22 , further comprising at least one of:
scheduling a second mobile station having a delay spread greater than a delay spread difference between the first beam pair and the second beam pair to receive data on the first beam pair after the base station switches transmitting data to the first mobile station from the first beam pair to the second beam pair;
inserting a quiet time for the first beam pair after the base station switches transmitting data to the first mobile station from the first beam pair to the second beam pair; and
inserting a large cyclic prefix for a symbol transmitted on the first beam pair after the base station switches transmitting data to the first mobile station from the first beam pair to the second beam pair.
25. The method according to claim 22 , wherein switching transmission of data from the base station to the first mobile station from the first beam pair to the second beam pair occurs at a slot boundary.
26. The method according to claim 22 , wherein the second beam pair has a delay spread greater than the cyclic prefix of the first beam pair.
27. The method according to claim 22 , wherein a duration of the cyclic prefix is selected from a plurality of predetermined durations for the cyclic prefix.